docs: def bucket_type(self, name):
          """
          Gets the bucket-type by the specified name. Bucket-types do
          not always exist (unlike buckets), but this will always return
          a :class:`BucketType <riak.bucket.BucketType>` object.
  
          :param name: the bucket-type name
          :type name: str
          :rtype: :class:`BucketType <riak.bucket.BucketType>`
          """
          if not isinstance(name, string_types):
              raise TypeError('BucketType name must be a string')
  
          btype = BucketType(self, name)
          return self._setdefault_handle_none(
                  self._bucket_types, name, btype)